: The objectives of the research proposed in this application are to investigate the fundamental cellular and molecular events that result in cytotoxic T lymphocyte (CTL) induction against herpes simplex virus (HSV) and to develop more effective means of vaccinating against HSV. The guiding hypothesis for the investigations is that the CTL response is important for immunity against HSV and that CTL induction, especially following immunization with DNA vaccines, involves cross priming/cross presentation between cells which produce antigen and those which present antigenic determinants to the specific responding CD8+ T lymphocytes. The specific aims are as follows: i) To define the cellular and molecular mechanisms by which cross presentation results in CTL induction in vitro. These studies should identify the mediators of cross presentation, the optimal conditions for their production, and the mechanisms by which the mediators elicit CTL. ii) A second aim is to assess the relative importance of cross priming versus direct priming. The in vivo mechanism of cross priming following DNA immunization will be compared to that which occurs in vitro as the means by which DNA vaccines succeed at inducing CTL responses in vivo. iii) Finally, since preliminary studies implicate a role for chaperone bound peptides as the mediators of cross priming/presentation, immunizing with chaperone peptides will be compared with standard immunization protocols for their efficacy at inducing CTL and protective antiviral immunity. Our experiments may identify better methods of generating protective immunity against HSV.